34 RESULTS WITH WHEAT 



Produce obtained. A comparison of the produce of 

 plots 3 and 5 shows that the long continued application of 

 superphosphate, with salts of potash, soda, and magnesia, has 

 produced very little increase in the wheat crop ; the average 

 produce on plot 5 during 40 years is, indeed, barely two 

 bushels greater than on plot 3, left continuously without 

 manure. The supply to the soil of the essential ash con- 

 stituents of the wheat crop thus entirely fails to yield a satis- 

 factory produce. 



The results obtained on the next series of plots, 6, 7, 8, 

 show that when ammonia salts are added to the superphos- 

 phate and alkalies the yield of wheat is immensely increased ; 

 indeed on plot 8, and sometimes on plot 7, the produce sur- 

 passes that given by fourteen tons of farmyard manure 

 applied annually to the same land since 1843. Wheat is thus 

 clearly a crop which may be greatly benefited by applica- 

 tions of ammonia salts, and such applications judiciously 

 employed are capable of yielding a very large produce. 



The long continued trials at Rothamsted teach us that the 

 effect of ammonia salts is not transient. The ammonia is not 

 to be regarded as a mere "stimulant," as some farmers sup- 

 pose, but as a valuable plant food. The beneficial results of 

 its application are apparently undiminished in the Rothamsted 

 wheat field by a continuous use of more than forty years. 

 The produce of each successive ten years during this period 

 will be found in Table V. The second ten years embraces 

 some particularly fine seasons, and the third ten years some 

 particularly bad ones ; the produce of the plots generally rises 

 and falls with the character of the seasons in this middle 

 period. On comparing the crops yielded during the fourth 

 period of ten years with those yielded in the first period, we 

 see that though the produce has distinctly fallen off on 

 those plots on which the exhaustion of some essential 

 constituent of plant food is in progress (plots, 3, 5, n, loa), 

 yet it is fully maintained on the three plots receiving a liberal 

 manuring of the ash constituents of the wheat crop, coupled 

 with an annual dressing of ammonia salts ; the average pro- 

 duce of plots 6, 7, 8, during the first ten years was in fact 32f 



